1997 Chevy Lumina won't strat

My chevy lumina won't start I turn the key and nothing. Have tried to boost batt, checked all fuses, charged batt. I have crossed the terminals on the starter and it cranks that way. I was told it was the key and the dealer told me it probably isn't that I should have the codes checked. All lights work and all guages work have tried it in neutral as well and it still won'tstart, any ideas?